The present invention relates to a method and a monitor apparatus for displaying parameters indicative of muscle relaxation.
Examples of measurement and monitoring items required for medical care of a patient undergoing surgical procedures include blood gases, movements of the circulatory system, respiration, anesthetic depth, and muscle relaxation. Among these items, parameters which can be monitored in a real time manner include electrocardiogram output, blood pressure, SpO2, body temperature, heart rate, respiratory rate, and the like.
Accordingly, monitoring a muscle relaxation state of a patient undergoing surgical procedures is also an extremely important issue. From the above viewpoint, a nerve stimulation system has conventionally been employed as an apparatus for monitoring a muscle relaxation state. The nerve stimulation system is configured so as to stimulate an ulnar nerve of a patient, and measure contraction of an adductor muscle of the thumb in response to the stimulation. As examples of an apparatus of this type for monitoring a muscle relaxation state, there has generally known an apparatus of a type which measures changes in a measured myogenic potential, and an apparatus of another type which measures kinetic effects deriving from muscle contraction (e.g., measuring an acceleration of muscular response).
The following methods have been adopted as stimulation patterns for detecting and measuring a muscle relaxation state by electric stimulator.
(1) Single Stimulation Method: a stimulation method of applying stimulating current of 200 microsecond at intervals of one or ten seconds, thereby applying single stimulation.
(2) TOF (train of four) Method: a stimulation method of applying stimulation trains at 15-second intervals, each train constituted of four repeated stimuli at 0.5 second intervals. In the TOF method, a ratio (a TOF ratio) between the height of the first stimulation and that of the fourth stimulation is expressed in %, which reaches 100% when the administered muscle relaxant is not exerting any effect.
(3) DBS (double burst signal) Method: a stimulation method of generating a stimulation train, generally constituted of three stimuli at 20 millisecond intervals, and another train after 0.75 second, thereby determining a difference in responses to these two burst signals by hand (palpation).
(4) PTC (post tetanic count) Method: a stimulation method to be employed when a response to the stimulation applied by the single stimulation method and the TOF method is completely faded under a state of deep muscle relaxation. First, stimulation at 1 Hz is applied for 15 cycles. When no response to the stimulation is ascertained, tetanic stimulation is applied. Subsequently, after three seconds, by stimulation at 1 Hz is applied for 15 cycles. Timing when a response to the TOF stimulation emerges next is estimated on the basis of the number of evoked responses.
(5) Tetanic Stimulation Method: a stimulation method of making an evaluation by palpation on the basis of tetanic stimulation, in accordance with which stimulation at 50 or 100 Hz is applied for only five seconds.
The related-art apparatus for monitoring and displaying muscle relaxation state has a function of simply displaying the timing of electric stimulation and a degree of a change in the acceleration of a muscle with respect to time. However, the apparatus involves a problem, in that it lacks a function of monitoring timing at which a muscular relaxant is administered, thereby being unable to ascertain a chronological relationship between administration of a drug and changes in an acceleration of a muscle. Therefore, the related-art apparatus of this type has failed to accurately ascertain a duration between administration of a drug and timing at which the drug starts to exert its effect, or the like.
In view of the above, Japanese Patent Publication No. 10-57320A discloses a monitor apparatus in which event data such as an event pertaining to administration of a muscle relaxant can be input, and there are displayed the timing that the event is occurred and a timing and a magnitude of a response of an electrically stimulated muscle.
However, in the above monitor apparatus, among parameters indicative of the muscle relaxation, such as a TOF ratio, a TOF count, and a PTC, are to be displayed on a monitor screen, only a single parameter is displayed in the form of a numerical value or a graph. Accordingly, it is impossible to determine a change in a muscle relaxation state continuously on the basis of the muscle relaxation parameters which are not displayed on the monitor screen.